For example, Patent Document 1 describes an invention of a saddle type fuel tank for storing fuel to be supplied to the internal combustion engine mounted on the vehicle, in the chamber having the saddle-shaped portion between the main chamber and the subchamber. In the vehicle in which on-board objects such as a propeller shaft and an exhaust pipe extending in a traveling direction of the vehicle are arranged across a tank body, the saddle type fuel tank is used as a measure for passing the on-board objects through the tank body without interfering with the tank body. The saddle type fuel tank according to Patent Document 1 is provided with a member called a fuel supply amount regulating valve (hereinafter referred to as a “full-tank regulating valve”).
The full-tank regulating valve according to Patent Document 1 is located at the saddle-shaped portion in the chamber of the tank body and is provided in an exhaust passage communicating the tank body and a canister. The full-tank regulating valve has a float valve inside a substantially cylindrical valve body. The float valve has a function of opening and closing a communication port of the exhaust passage based on a magnitude of a first pressure difference Pdif1 (Pdif1=|Pvalve−Ptank|) between an internal pressure Pvalve in the valve body and an internal pressure Ptank in the tank body. An orifice for communicating the inside and outside of the valve body is provided close to the float valve in a side wall of the valve body.
In the saddle type fuel tank according to Patent Document 1, a substantially cylindrical hanging pipe offset toward a subchamber and extending obliquely downwardly is communicatively connected to a lower end of the substantially cylindrical valve body of the full-tank regulating valve. An opening of the hanging pipe is provided at a height corresponding to a full-tank liquid level.
The full-tank regulating valve according to Patent Document 1 configured as described above operates as follows. When a fuel liquid surface reaches the full-tank liquid level, that is, the opening of the hanging pipe during refueling of the tank body, the opening of the hanging pipe in the valve body is closed by the fuel liquid surface. As a result, the internal pressure Pvalve in the valve body is isolated from the internal pressure Ptank in the tank body. Assume that even after the fuel liquid surface reaches the full-tank liquid level, refueling continues.
Then, the internal pressure Pvalve in the valve body becomes lower than the internal pressure Ptank in the tank body, because the exhaust passage is open. The fuel runs up through the hanging pipe so as to reduce the first pressure difference Pdif1. Finally, the first pressure difference Pdif1 exceeds a predetermined internal pressure threshold value Pth (Pdif1>Pth). In response to this, the float valve closes the exhaust passage.
Meanwhile, when the exhaust passage is closed, external air (internal air in the tank body) of the valve body flows into a chamber of the valve body through the orifice so as to reduce the first pressure difference Pdif1. This inflow causes the first pressure difference Pdif1 to converge to the internal pressure threshold value Pth or less. Then, the float valve opens the exhaust passage.
In short, the full-tank regulating valve is configured to restrict a fuel supply amount by opening and closing the communication port of the exhaust passage based on the magnitude of the first pressure difference Pdif1 between the internal pressure Pvalve in the valve body and the internal pressure Ptank in the tank body.